One some multi-engine aircraft, engine-induced acoustic resonance can be generated, resulting in noise and sometimes vibration being transmitted into the aircraft cabin. The resulting noise and vibration can lead to passenger discomfort. Known approaches to controlling noise and vibration include matching the rotational speeds and phase relationships of the aircraft engines. In many of these known approaches, one engine is selected as a “master” engine and the other as a “slave” engine. When a speed mismatch of sufficient magnitude occurs, the engine speed of the “slave” engine is adjusted to equal that of the master engine.
In the case of multi-spool engines, such as turbofan, turboprop or prop-fan gas turbine engines, only a single spool is typically synchronized. Typically, the speeds of the fan spool (N1) are synchronized. However, the speeds of the high pressure spools (N2) remain non-synchronized, resulting continued generation of undesirable noise and/or vibration. Attempts have been made to synchronize both N1 and N2 speeds in multi-spool engines. Some current approaches rely on closed-loop control of N2 speed based on sensed N2 speed and or one or more other engine parameters. These approaches can exhibit stability issues. Another approach has been to attempt to precision balance the engines prior to installation. This approach can be time-consuming and costly.
Hence, there is a need for reducing engine-induced aircraft cabin resonance that does not rely on closed-loop N2 control and/or does not rely on precision engine balancing. The present invention addresses at least this need.